This invention relates to a carrier tape, and more particularly to a carrier tape of a COF (Chip On Film) type and its manufacturing method.
Carrier tapes, in which a plurality of flexible wiring substrates are continuously formed along their length, include those of a so-called TAB (Tape Automated Bonding) type and of a so-called COF (Chip On Film) type. The TAB type carrier tape includes a base film having through holes formed in portions near portions on which integrated circuits are formed, and formed in portions near outer leads. The COF type carrier tape includes a base film with no through holes formed in portions near portions on which integrated circuits are formed. These carrier tapes are widely used for the connection of, for example, drivers for use in liquid crystal display devices.
In the TAB type carrier tape, the base film is thick, and is bent at portions on which outer leads are provided, thereby connecting the outer leads to the terminals of an external circuit. To enhance the flexibility of the tape, through holes are formed in those portions of the base film which are located under the outer leads. On the other hand, in the COF type carrier tape, the base film, which is made of polyimide, is relatively thin and highly flexible. Therefore, no through holes are formed in portions of the tape near portions on which integrated circuits are formed.
As is shown in FIG. 35, a carrier tape 21 of the COF type has a plurality of corresponding sprocket holes formed along both left and right side portions of a base film 22, wirings 24 provided on middle surface portions of the base film 22, and protective films 25 each covering corresponding wirings 24 except for opposite terminal portions thereof. The base film 22 is as long as between several tens m to 100 m. After forming the sprocket holes, the base film is subjected to a roll-to-roll treatment using pin rollers.
Since the TAB type base film is generally formed of a polyimide film with a relatively thick thickness of about 75 to 125 xcexcm, the base film can have a sufficient strength even at portions near the sprocket holes. Accordingly, the pins of the pin roller are reliably engaged with the sprocket holes, thereby enabling smooth transfer of the carrier tape by the pin roller without deforming the sprocket holes.
However, there is a case where a relatively thin film with a thickness of 38 xcexcm or less is used as the COF type base film 22. In this case, the base film 22 does not have sufficient strength at portions near the sprocket holes 23. Therefore, it is difficult to suitably engage the pins of the pin roller with the sprocket holes 23. Even if the pins may be engaged with the holes, the carrier tape is liable to come away from the pins while it is transferred, and the four corners of each sprocket hole are liable to tear because of mechanical stress that concentrates on the portions of the carrier tape near the sprocket holes while the tape is transferred by the pins. The tears are liable to enlarge, which will cause displacement of the carrier tape 21 and hence will adversely affect the degree of alignment in a later process.
It is an object of the invention to enable smooth transfer, by a pin roller, of a carrier tape having a relatively thin base film, in particular, a COF type carrier tape, without deforming sprocket holes formed in the tape.
It is another object of the invention to provide a manufacturing method for realizing a high productivity of carrier tapes that can reliably be transferred by a pin roller.
To attain the first object, there is provided a carrier tape for connecting an integrated circuit to an external circuit, comprising a reinforcing layer formed on one surface of a base film, and having an opening corresponding to one of holes formed in the base film, the opening having a side facing a direction of a length of the base film and exposing a side portion of the one surface of the base film, the side portion located at the side of the opening. Even if the base film is relatively thin, the reinforcing layer imparts a substantially desirable strength to a portion of the base film near each hole, thereby enabling smooth transfer of the base film by a pin roller without deforming the base film. Further, forming the opening of the reinforcing layer larger than the holes of the base film makes it difficult to bring the pins of the pin roller into contact with the reinforcing layer. As a result, generation of particles when the pins contact the reinforcing layer is minimized, thereby preventing shortcircuiting due to the presence of the particles if the reinforcing layer is formed of a conductive material.
To attain the other object, there is provided a method of manufacturing a carrier tape for connecting an integrated circuit to an external circuit. In this method, reinforcing layers are formed on one surface of a base film such that they have openings corresponding to holes formed in the base film, each of the openings having one-side facing a direction of a length of the base film and exposing one-side portion of the one surface of the base film, the one-side portion located at the one-side of the opening. Accordingly, even if the carrier tape is of the COF type and its base film is relatively thin, the reinforcing layers impart a substantially desirable strength to a portion of the base film near each hole, thereby enabling smooth transfer of the base film by a pin roller without deforming the base film. The openings are formed in the side portions of the reinforcing layer, which are located in the direction of the length of the base film, so as to prevent the pins of the pin roller from contacting the reinforcing layer while the pin roller transfers the base film. This is particularly effective if the reinforcing layer is formed of a conductive material, since particles of the conductive material may cause shortcircuiting of wiring.
Moreover, there is provided another method of manufacturing a carrier tape for connecting an integrated circuit to an external circuit, comprising the steps of: forming wires on one surface of an elongated base film in a central portion of each of carrier-tape-forming areas which are each defined on the one surface and have holes formed in width-directionally opposite portions thereof; and forming reinforcing layers on the one surface of the base film, the reinforcing layers having openings corresponding to the holes of the base film, the openings exposing one-side portions of the one surface of the base film, which are located in a direction of a length or a width of the base film. Accordingly, a plurality of carrier tapes can be manufactured simultaneously, which increases the productivity.
In the step of forming the reinforcing layers in the above method, adjacent reinforcing layers formed in adjacent carrier-tape-forming areas separate from each other by a predetermined distance, so as not to form no reinforcing layer on those portions of the base film at which the base film is cut to be divided into a plurality of carrier tapes. Therefore, no particles will be generated from the reinforcing layers while the base film is cut by, for example, a roll cutter.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.